The present invention relates to a blood-culture flask 1 with an integrated subculture comprising a flask 2 proper that can be filled with a liquid nutrient solution and has a neck 3 with an outside thread 5, a support 6 that can be coated with a solid culture medium 25, a resilient stopper 7 with an edge that projects at one end, and a screw cap 9.
Detecting the presence of microorganisms in body fluids, especially of bacteria in the blood, by innoculating a liquid nutrient medium with the patient's blood to enrich the nutrient with any pathogens that may be present and then allowing growth on a solid culture medium is generally common.
What are called two-phase blood-culture flasks, in which both culture media are combined into a closed system in one container in order to prevent the otherwise conventional labor-intensive subculturing and avoid the usually inescapable risk of contamination, have been available for a long time for this purpose.
These culture flasks are triangular, rectangular, or hexagonal glass bottles that are filled to about one half or one third with liquid nutrient medium and are coated on one side with a solid nutrient medium. All of the flasks have some sort of air-tight seal that can be penetrated with a hypodermic needle or similar device. They must not be opened during the innoculation. They are described by M. Castaneda-Ruiz in "Practical method for routine blood cultures in brucellosis," Proc. Soc. Exp. Biol Med. 64, 114-15 (1947) and are called Castaneda flasks, two-phase Hemoline-Trypcases, or Vacuneda flasks in the literature of various manufacturers.
The solid culture phase in the aforesaid systems always extends down over the total height of one side of the flask into the liquid culture phase and is accordingly always in contact with the liquid phase when the flask is standing erect. The constant contact between the phases results in an exchange of contents, with the liquid nutrient solution becoming cloudy and the color and/or consistency of the layer of solid nutrient altering. This process is especially undesirable when boiled blood agar, which is especially sensitive to lixiviation by the liquid phase, is employed. Although boiled blood agar is an especially practical nutrient agar for blood subcultures, especially for culturing demanding microorganisms, it cannot be employed in the aforesaid closed two-phase systems for the reasons just described.
Although this drawback is admittedly avoided in accordance with German Utility Model No. 8 309 876, by employing a two-phase bottle that has a culture-medium adjunct in the form of a bay-like convexity at the top of one side, so that the solid culture-medium phase located within it is positioned above the level of the liquid nutrient medium to prevent undesired contact between the two phases as long as the flask is maintained erect, it is relatively difficult and expensive to manufacture not only this type of flask but also other types to the extent that they involve concavities and interior ribs to secure the culture medium.
Furthermore, all of these types of culture flasks entail a common drawback in that the solid culture-medium phase cannot be removed subsequent to cultivation of the flask.
German Patent No. 2 806 902 describes a system that consists of two separate containers, with the liquid culture medium in one and the solid nutrient phase in the other. Each container is separate from the other and separately sealed before being used. In use, each container must be opened and, subsequent to innoculation of the liquid culture medium, connected together with a sealing ring, preferably made out of polyethylene. The container with the solid culture medium is at that time relatively higher than the other container. The support for the solid culture medium is a sort of microscope slide.
Although this system does eliminate the drawbacks of constant contact between the solid and liquid phases and of manufacturing expense, it entails still other drawbacks. The necessity of opening both containers subsequent to innoculation involves the risk of secondary contamination.
The necessary opening of the container with the fluid medium allows air into the container and impedes the detection of obligatorily anaerobic pathogens. Nor can capnophilic bacteria, bacteria that depend on carbon dioxide, be detected, because the support with the solid culture medium is located only at the top, whereas the heavy carbon dioxide is present only at the very bottom. Thus the growth of anaerobic and capnophilic pathogens is very unsatisfactory in such a system.
German OS No. 1 959 902 describes a closed two-phase blood-culture flask into which a supporting tray for accommodating solid culture media is inserted and that is completely sealed with a rubber stopper and screw cap.
This is accordingly a closed system that is innoculated while evacuated, that can be cultivated with or without air, and from which the solid culture medium can be removed subsequent to cultivation. The tray is made out of cast resin, glass, or another ceramic material and has a hollow, cylindrical end positioned in the opening in the neck of the bottle, establishing a friction seal. The space inside the cylinder is filled by a resilient stopper with an upper edge that rests against the upper edge of the cylindrical end. The ensemble can be covered with a screw cap. This culture flask, however, entails the drawback that the bottle cannot be sealed 100% tight with a friction seal between the cylindrical end of the supporting tray and the neck of the flask, both of which are made of rigid materials. Nor does the edge of the resilient stopper that projects out at the top suffice to completely seal the bottle, so that air can penetrate into or gas escape from a bottle that has been evacuated or contains a particular gas.
Since the supporting tray extends over the whole height of the flask, this culture flask also has the drawback initially described in relation to known two-phase blood-culture flasks in that the solid culture medium is always in contact with the liquid culture medium when the bottle is erect.
Another disadvantage is that the supporting tray is coated on only one side and, unless the side is divided with partitions, different culture-medium compositions cannot be employed as is necessary for differential microorganism growth. Although the document does describe one embodiment in which the supporting tray is divided into different sections by webs, the areas of the sections are so small that the embodiment is not appropriate for practical applications.
Finally, there is another drawback in that the support, which consists of the tray and cylindrical end, is extremely complicated from an engineering standpoint and hence relatively expensive.